1. Field of the Invention
The present invention relates to a method and an apparatus for producing plant nutritive pellets from the sludge arising from wastewater treatment.
2. Description of the Related Art
The major part of all sludge from wastewater treatment plants is deposited on garbage dumps in spite of the sludge containing valuable plant nutrition. The reason for this is not primarily fear of heavy metals in the sludge but, above all, the difficulties farmers have in dealing with such sludge continuously. Previously, attempts have been made to form the sludge into pellets directly but this has been found impossible, since the mass has too loose a structure, because of its high (70-80%) water content. Getting below this water content percentage has been found to be impossible in the sludge handling process, since most of the water in the sludge is cell-bound. In addition, it is very sticky, resulting in that any pellets formed quickly stick together and form large aggregates. It is almost impossible to dry out these large lumps to a sufficiently low water content for storage. These masses are also an infection hazard, since they always contain infectious organisms and substances, e.g. salmonella bacteria, different viruses and parasite eggs.